This invention concerns temperature indicators and, more particularly, although not exclusively, devices for providing a lasting indication of a temperature threshold having been exceeded.
It is commonplace in engineering applications to measure operating temperatures using sensors, such as thermocouples or the like, that can provide an electrical output indicative of a temperature reading. Thus records of past operating temperature readings can be stored as data files for later access. The sensing element of such devices operates in a transient manner such that its physical state is constantly changing to current conditions. As such, a physical state of the sensor itself that is indicative of a previous temperature reading is lost in favour of a current state.
There exist a number of applications in which it is not possible, or highly problematic, to use such conventional sensors and/or in which a suitable wired or wireless data connection is not available. One such example concerns sealed reaction chambers or other enclosures/conduits that are required to be electrically isolated for safety reasons. Even if conventional sensors can be used, it may be necessary to electrically isolate the equipment as part of a safety procedure such that temperature readings can no longer be taken.
In other applications it is possible that a thermocouple or other temperature sensor is required to be sensitive over a normal operating range but may fail if a maximum temperature threshold is exceeded. Furthermore for large and/or complex systems, it may simply not be cost-effective or practical to provide conventional temperature sensors for all components or areas of the system.
In any of the above scenarios it is desirable to be able to record a maximum temperature reached by a component or fluid flow, e.g. a working fluid, coolant or the like, within the system. Such a temperature reading may provide useful engineering information for diagnosing a fault or failure mode of equipment both in a test environment as well as in the field.
It is an aim of the invention to provide a temperature indicator device which can accommodate environments or scenarios in which the use of conventional sensors is problematic. It may be considered a further aim of the invention to provide temperature indicator that can provide avisual indication of maximum temperature to which the indicator has been exposed even after the temperature has subsequently subsided.